Defibrillation Thresholds and Perioperative Mortality Associated with Endocardial and Epicardial Defihrillation Lead Systems

Defibrillation thresholds (DFT) and perioperative mortality were evaluated in 123 patients who had endocardial defibrillation leads implanted in conjunction with the Medtronic model 7216A/7217 (Medtronic, Inc.) cardioverter-defibrillator (ICD). Clinical variables, implant DFTs, and 30-day perioperative mortality were compared with 266 patients who had the ICD implanted with epicardial defibrillation leads. The two groups were comparable in age, gender, and incidence of coronary artery disease. New York Heart Association Class I and II were more frequent in patients with endocardial leads (87.7%) as compared to those with epicardial leads (78.8%; P < 0.001). Mean left ventricular ejection fraction was significantly higher in patients with the endocardial lead system (37% vs 33%; P < 0.05). A significant proportion of patients with epicardial lead systems underwent another cardiac surgical procedure at the time of ICD implantation (13.9%) as compared to none in those who had endocardial leads implanted (P < 0.001). All patients with endocardial leads had implantation of triple lead systems as compared to 53.4% with epicardial leads (P < 0.001). The mean DFT at implant was lower in epicardial lead recipients (8.9 J) as compared to endocardial lead recipients (13.3 J; P < 0.001). Perioperative mortality had a significant trend to lower risk for endocardial lead systems (0.8%) as compared to epicardial systems (4.2%; P = 0.07). We conclude that this endocardial lead system has additional electrode and higher defibrillation energy requirements than the epicardial lead systems used with the Medtronic pacemaker ICD. However, the use of endocardial nonthoracotomy defibrillation leads is associated with a markedly reduced perioperative risk of ICD implantation. This could be due to patient characteristics, a less invasive implant procedure, and absence of concomitant cardiac surgery.     

Experience with Two Different Nonthoracotomy Systems for Implantable Defibrillator in 170 Patients

Implantation of a nonthoracotomy system (Medtronic PCD or CPI Endotak) was attempted in 170 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) not requiring concomitant cardiac surgery. A nonthoracotomy system could be successfully implanted in 95 of the 115 patients with the PCD system and 49 of 55 patients receiving the Endotak lead system. In 26 patients with failed nontboracotomy system because of defibrillation threshold (DFT) > 25 joules (J), an epicardial system was implanted at the same setting. Patients receiving the two lead systems were comparable with regard to age, sex, and ejection fraction. However, since tbe PCD system offers tiered therapy multiprogrammable options, all attempts were made to implant tbis lead system in patients with VT that could be pace terminated. Mean DFT(15 ± 4.7 vs 17 ± 4.6 J;P = 0.03) and implant time (2.5 ± 0.6 vs 3.3 ± 0.7 hours; P = 0.02) were less with the Endotak lead system. There was no perioperative mortality. During a mean follow-up of 20 ± 4 months, there were eight instances of lead dislodgment in patients receiving the PCD system. Tbere were four nonsudden cardiac deaths and one sudden death in the Endotak group and three nonsudden deaths in the PCD group. Sudden cardiac death and total survival using the intention-to-treat analysis during this follow-up period were 99% and 95%, respectively. In conclusion, successful implantation, perioperative mortality, and survival rate are comparable with both lead systems; however, incorporating two defibrillating electrodes in one lead minimizes lead dislodgment and reduces implant time.     

Subpectoral Implantation of ICD Generators: Long-Term Follow-Up

A nonthoracotomy surgical approach using an endocardial electrode and combined implantation of a subcutaneous patch and the implantable cardioverter defibrillator (ICD) generator in a Subpectoral pocket has been described. We report the long-term follow-up results in patients undergoing implantation using this approach. The patient population consisted of 28 patients (22 men and 6 women) with a mean age of 59 ± 12 years. The underlying heart disease consisted of coronary artery disease in 20 patients and dilated cardiomyopathy in 8 patients. Sustained ventricular tachycardia was the mode of presentation in 16 patients and sudden cardiac death in 12 patients. The mean left ventricular ejection fraction was 31%± 6%. The lead system consisted of an 8 French bipolar passive fixation rate sensing lead positioned at the right ventricular apex, an 11 French spring coil electrode positioned at the superior vena cava-right atrial junction (surface area 700 mm²), and submuscular placement of a large patch (surface area 28 cm²) on the anterolateral chest wall near the cardiac apex via a submammary incision. A defibrillation threshold of ≤ 15 joules (J) was required for implantation. This criterion was not satisfied in five patients; thus, a limited thoracotomy was performed via the submammary incision, and the large patch was placed epicardially. The mean R wave amplitude was 12 ± 3 mV, the mean pacing threshold was 1.0 ± 0.5 V at 0.5 msec, and the mean defibrillation threshold was 12.6 ± 3 J. ICD generators implanted were the Ventak-P in 17, PCD-7217 in 5, and the Cadence V-l00 in 6 patients. These patients have been followed for a mean of 14.6 ± 6 months. There was no perioperative mortality, and none of the patients developed an infection during follow-up. Generator migration or significant discomfort requiring ICD repositioning was not observed, although one patient developed an erosion requiring surgical repair.Conclusions: Subpectoral implantation of the ICD generator is feasible and was well tolerated by all patients with an acceptable complication rate (3.5%). As the size of future generation ICDs is reduced, subpectoral implantation may become the preferred approach.     

Short-and Long-Term Performance of a Tripolar Down-Sized Single Lead for Implantable Cardioverter Defibrillator Treatment: A Randomized Prospective European Multicenter Study

A new, thinner (10 Fr) and more flexible, single-pass transvenous endocardial ICD lead, Endotak DSP, was compared with a conventional lead, Endotak C, as a control in a prospective randomized multicenter study in combination with a nonactive can ICD. A total of 123 patients were enrolled, 55 of whom received a down-sized DSP lead. Lead-alone configuration was successfully implanted in 95% of the DSP patients vs 88% in the control group. The mean defibrillation threshold (DFT) was determined by means of a step-down protocol, and was identical in the two groups, 10.5 ± 4.8 J in the DSP group versus 10.5 ± 4.8 J in the control group. At implantation, the DSP mean pacing threshold was lower, 0.51 ± 0.18 V versus 0.62 ± 0.35 V (p < 0.05) in the control group, and the mean pacing impedance higher, 594 ± 110 Ω vs 523 ± 135 Ω (p < 0.05). During the follow-up period, the statistically significant difference in thresholds disappeared, while the difference in impedance remained. Tachyarrhythmia treatment by shock or antitachycardia pacing (ATP) was delivered in 53% and 41%, respectively, of the patients with a 100% success rate. In the DSP group, all 28 episodes of polymorphic ventricular tachycardia or ventricular fibrillation were converted by the first shock as compared to 57 of 69 episodes (83%) in the control group (p < 0.05). Monomorphic ventricular tachycardias were terminated by ATP alone in 96% versus 94%. Lead related problems were minor and observed in 5% and 7%, respectively. In summary, both leads were safe and efficacious in the detection and treatment of ventricular tachyarrhythmias. There were no differences between the DSP and control groups regarding short- or long-term lead related complications.     

The Subcutaneous Array: A New Lead Adjunct for the Transvenous ICD to Lower Defibrillation Thresholds

Despite the benefits of transvenous implantable cardioverter defibrillators (ICDs), concern exists that patients with high defibriliation thresholds (DFTs) have an inadequate safety margin between the DFT and the maximum defibrillator energy. A new transvenous ICD lead adjunct, a subcutaneous lead array (SQ Array), was developed to increase safety margins by lowering DFTs. Composed of three lead elements joined in a common yoke, the SQ Array is tunneled subcutaneously in the left lateral chest. Serving as their own controls, 20 patients were studied intraoperatively comparing transvenous lead-alone DFTs with lead-SQ Array DFTs. Seventeen males and three females were randomized to receive the SQ Array through the CPI Ventak PBx/Endotak 70 series protocol. Mean patient age was 63.7 ± 2.5 years and mean ejection fraction 0.34 ± 0.04. DFTs were determined using a precise protocol of step-down/step-up testing commencing at 20 joules. Lead-alone DFTs were tested using the proximal coil as the anode (+). For the lead-SQ Array, the proximal coil and the array were linked as a common anode. The icad-SQ Array resulted in a statistically significant reduction in mean monophasic DFT from 23.3 ± 2.3 joules (lead-alone) to 13.5 ± 1.9 joules (lead-SQ Array) (P < 0.001). Six patients had lead-alone DFTs > 25 joules but did not require thoracotomy because of adequate DFT reduction with the SQ Array. We conclude that the SQ Array adjunct to the transvenous ICD lead lowers monophasic DFTs an average of 9.8 joules (40.6%) obviating the need for a thoracotomy in selected patients .     

Epicardial and Nonthoracotomy Defibrillation Lead Systems Combined with a Cardioverter Defibrillator

The intraoperative and long-term results were reviewed in 67 patients who underwent implantation of the Ventritex Cadence defibrillator with either epicardial patch (EPI, 25 patients) or nonthoracotomy CPI Endotak (ENDO, 42 patients) defibrillation lead systems. In the ENDO group, 35 patients (83 %) had a defibrillation threshold (DFT) of ≤ 20 joules and did not require a subcutaneous patch. Intraoperatively, the DFT was 13 ± 9 joules (mean ± SD) for EPI and 15 ± 8 joules for ENDO (P = NS). There was no perioperative death in either group. During a mean follow-up of 12 ± 8 months, there was no sudden death, and four patients died from congestive heart failure (3 EPI, 1 ENDO). During follow-up, 875 spontaneous arrhythmia episodes (AE) occurred in 15 of 25 EPI patients (60%). versus 652 in 28 of 42 ENDO patients (67%; P = NS). Ventricular tachycardia at a rate ≥ 222 beats/min or ventricular fibrillation represented 167 AE for EPI (19%) and 182 AE for ENDO (28%), and was terminated by the first shock in 76% and 75% of attempts, respectively. Ventricular tachycardia at a rate ≥ 222 beats/min represented a total of 1,178 AE and antitachycardia pacing was successful in 660 of 708 AE (93%) with EPI and 414 of 470 AE (88%) with ENDO lead systems (P= NS). Therefore, a nonthoracotomy approach using the Cadence V-100 is safe and effective and has clinical results that are not significantly different from epicardial defibrillation lead systems.     

Effect of Biphasic Waveform Pulse on Endocardial Defibrillation Efficacy in Humans

Several clinical studies have proved increased defibrillation efficacy for implantable cardioverter defibrillators with biphasic pulse waveforms compared to monophasic pulse waveforms. This difference in defibrillation efficacy depends on the type of defibrillation lead system used. The influence of biphasic defibrillation pulse waveforms on the defibrillation efficacy of purely endocardial defibrillation lead systems has not yet been sufficiently examined, we, therefore studied 30 consecutive patients with drug refractory ventricular tachyarrhythmias during the implantation of a cardioverter defibrillator. After implanting an endocardial "integrated" sensing/defibrillation lead we performed a prospective randomized comparison of the defibrillation efficacy of monophasic and biphasic defibrillation waveform pulses. For endocardial defibrillation with the biphasic waveform the mean defibrillation threshold was 12.5 ± 4.9 joules and for the monophasic waveform 22.2 ± 5.6 joules (P < 0.0001). There was a decrease in the required defibrillation energy of biphasic defibrillation in 29/30 patients. Thus considering purely endocardial defibrillation a statistically significant and clinically relevant increase in defibrillation efficacy can be demonstrated for biphasic defibrillation waveform pulses.     

Defibrillation Energy Requirements with Single Endocardial (Endotak™) Lead

The need for thoracotomy in usually high risk patients has limited the use of the implantable cardioverter defibrillator. Initial clinical results with endocardial and subcutanous patch electrodes (SQPs) are en couraging. Using a single endocardial lead in the absence of a SQP for chronic implantation of the cardioverter defibrillator, the goal of the study was to obtain defibrillation thresholds (DFTs) of 15 Joules (J) or less and to investigate changes in DFT over time. We tested 19 consecutive patients (15 men, 4 women] age 62 ± 8.5 years with malignant ventricular arrhythmias (14 VT/5 VF). The underlying heart disease was coronary artery disease in 15 pafients, dilative cardiomyopathy in two patients, and primary electricaJ disease in two patients. Four patients had undergone previous cardiac surgery. Left ventricular ejection fraction ranged between 14% and 66% (39%± 12.6%). Pacing thresholds (0.54 ± 0.17 Vat 0.5 msec), R wave amplitude for pacemaker sensing (14.2 ± 7.0 mV), slew rate (2.12 ± 1.4 V/sec), and resistance (500.3 ± 73.9 W) were sufficient in all patients. Eighteen patients met our endocardial impiant criteria with a DFT ≤ 15 J (10.05 ± 4.03 J) using monophasic (14 patients) or biphasic (four patients) pulse wave forms. In the one remaining patient, with a DFT of 20 J, we implanted a SQP but there was no reduction of the DFT. All patients tested showed successful defibrillation prior to discharge. During follow-up of 88 patient-months (1–9 months), 114 spontaneous VT/VF episodes occurred in five patients and were all successfully terminated. Eleven patients with a minimum follow-up of 2 months were reassessed. In seven out of 11 patients, termination of VF was achieved with the same minimal energy requirements obtained intraoperatively. In three patients, DFT increased by 5 J (one patient) and 10 J (two patients). In a further patient, X ray revealed dislocation of the endocardial lead. Our data suggest that effective defibrillation is feasible with a single endocardial lead for implantation of cardioverter defibrillator. In addition, we strongly recommend repetitive x-ray control to detect asymptomatic lead dislocation. Despite stable DFTs in most of our patients, an energy difference of ≤ 15 J between acute DFT and cardioverter defibrillator energy rating seems to be currently desirable to ensure successful postoperative defibrillation.     

Long-Term Survival and Complications in Patients With Malignant Ventricular Tachyarrhythmias: Treatment With a Nonthoracotomy Implantable Cardioverter Defibrillator With or Without a Subcutaneous Patch

The Endotak lead system and ICD has been used to treat patients with malignant ventricular arrhythmias. We analyzed The clinical characteristics of 1,053 patients who underwent implantation of The Endotak lead system with or without a subcutaneous patch. Group A consisted of 567 patients receiving The Endotak lead with a subcutaneous patch: group B consisted of 486 patients receiving The Endotak lead alone. The 2-year survivals from sudden death, cardiac death, and total death in groups A and B were 97.6%/98.2% (P = 0.38), 88.6%/92.7% (P = 0.09), and 84.7%/86.8% (P = 0.06). respectively. Minimum tested effective defibrillation energy at implantation was 17.2 ± 5.2 J for group A and 15.8 ±5.1 J for group B (P < 0.01). The operative mortality was 1.8% in group A and 0.6% in group B (P = 0.09). The incidence of lead dislodgment, malfunction, and infection was 6,7% for group A and 3.5% for group B (P < 0,01), Sudden death survival was excellent in both groups with less lead complications in group B. The Endotak lead alone may be The preferred choice of lead configuration in those patients who have adequate defibrillation thresholds at implant. (PACE 1997: 20[Pt. I]:1305-1311)     

Prospective Randomized Comparison of Biphasic Waveform Tilt Using a Unipolar Defibrillation System

Background: A unipolar defihrillation system using a single right ventricular (RV) electrode and the active shell or container of an implantable cardioverter defibrillator situated in a left infraclavicular pocket has been shown to be as efficient in defibrillation as an epicardial lead system. Additional improvements in this system would have favorable practice implications and could derive from alterations in pulse waveform shape. The specific purpose of this study is to determine whether defibrillation efficacy can be improved further in humans by lowering biphasic waveform tilt. Methods: We prospectively and randomly compared the defibrillation efficacy of a 50% and a 65% tilt asymmetric biphasic waveform using the unipolar defibrillation system in 15 consecutive cardiac arrest survivors prior to implantation of a presently available standard transvenous defibrillation system. The RV defibrillation electrode has a 5-cm coil located on a 10.5 French lead and was used as the anode. The system cathode was the active 108 cm² surface area shell (or “CAN”) of a prototype titanium alloy pulse generator placed in the left infraclavicular pocket. The defibrillation pulse derived from a 120-μF capacitor and was delivered from RV ± CAN, with RV positive with respect to the CAN during the initial portion of the cycle. Defibrillation threshold (DFT) stored energy, delivered energy, leading edge voltage and current, pulse resistance, and pulse width were measured for both tilts examined. Results: The unipolar single lead system, RV ± CAN, using a 65% tilt biphasic pulse resulted in a stored energy DFT of 8.7 ± 5.7 J and a delivered energy DFT of 7.6 ± 5.0 J. In ail 15 patients, stored and delivered energy DFTs were < 20 J. The 50% tilt biphasic pulse resulted in a stored energy DFT of 8.2 ± 5.4 J and a delivered energy DFT of 6.1 ± 4.0 J;P = 0.69 and 0.17, respectively. As with the 65% tilt pulse, all 15 patients had stored and delivered energy DFTs < 20 J. Conclusion: The unipolar single lead transvenous defibrillation system provides defibrillation at energy levels comparable to that reported with epicardial lead systems. This system is not improved by use of a 50% tilt biphasic waveform instead of a standard 65% tilt biphasic pulse. (PACE 1995; 18:1369–1373)     

Intracardiac Emergency Defibrillation for Refractory Ventricular Fibrillation During Implantation of Cardioverter Defibrillators with Nonthoracotomy Lead Systems

Implantable cardioverter defibrillators (ICDs) are being implanted in increasing numbers. At inlraoperative defibrillation threshold tests refractory ventricular fibrillation (VF) requiring emergency open chest resuscitation is a major concern during impiantation of nonthoracotomy ICD lead systems. A new method of high energy endocardial/extrathoracic defibrillotion via the implanted ICD transvenous defibrillation electrode (TDE) was used to terminate refractory VF. During implantation of ICD with TDE in 20 patients refractory VF occurred in two patients. The arrhythmia was terminated with endocardial/extrathoracic defibrillation in both cases, and no complications were observed.     

Initial Experience with a New Transvenous Defibrillation System

The clinical efficacy and safely of a new bidirectional transvenous defibrillation endocardial lead system (ELS) was studied in 39 patients with ventricular tachycardia (VT) or fibrillation (VF). There were 28 patients with coronary disease and 11 patients with nonischemic VT/VF. Fourteen patients received the ELS combined with antitachycardia pacing devices (Ventak PRx 1700, CPI) and 25 patients with the Ventak P or P2 (CPI). Implantation of the ELS was attempted in 47 patients. Intraoperatively, the mean defibrillation threshold (DFT) was > 25 joules in five patients and no reliable ELS position was found in three other patients. These eight patients underwent thoracotomy and epicardial leads implantation. The mean DFT was ≤ 20 jouJes in all 39 patients and the mean DFT was 18 joules. During the mean follow-up of 8 ± 2 months two patients (5%) died suddenly. Complications occurred in two patients (5%).     

Long-Term Stability of Defibrillation Thresholds with Intrapericardial Defibrillator Patches

From March 1982 to May 1, 1992, 105 consecutive patients underwent initial implant of cardioverter defibrillators (ICD) at our institution. Twenty-nine patients (23 male and 6 female, average ejection fraction 32.24%) with ICD systems implanted via thoracotomy and either intra- or extrapericardial patches, had one or more revisions including 56 generator changes or staged implant procedures, three patch revisions, one patch lead fracture without revision, and one sensing lead revision. The time between pulse generator revisions averaged 19.5 months. Initial defibrillation threshold mean was 12.8 joules (n = 25); at first revision, 14.46 joules (n = 29), (P = NS); by fifth revision, 15.0 joules (n = 2), (P = NS). One patch was noted to be crinkled at 70 months; one patch had migrated by 39 months, and two patch leads had fractured at the costal margin by 69 and 90 months. One patient with marginal defibrillation thresholds had an additional patch placed at revision to an upgraded ICD unit. Once acceptable defibrillation threshold (DFT) is obtained, the long-term intrapericardial DFT remains stable unless a specific problem occurs. As a small, nonstatistically significant increase in DFT may occur, caution must be exercised in patients with marginal DFTs.     

Transesophageal Defibrillation: Animal Studies and Preliminary Clinical Observations

Ventricular fibrillation (VF) that fails to respond to transthoracic defibrillation leaves the clinician with few alternatives. The purpose of this study was to develop a technique of rescue defibrillation by use of transesophageal electrodes. Fourteen anesthetized dogs (20 30 kg) were investigated in this study. Two electrodes (300 mm²) were mounted 8 cm apart on an esophageal probe and inserted approximately 40 cm from the mouth. VF was induced using AC current delivered to the myocardium. Defibrillation was then performed between the distal electrode (anode) and anterior skin patch (cathode). After 15 seconds of induced VF, transesophageal and transthoracic defibrillation thresholds (DFTs) were determined in random order. The esophageal DFT (90 ± 15 joules) tended to be lower than the transthoracic DFT (115 ± 35 joules), though this difference was not statistically significant. One dog could not be defibrillated by transthoracic defibrillation but responded to transesophageai defibrillation. Esophageal electrodes were also useful for arrhythmia discrimination and ventricular pacing (pacing threshold of 38 ± 5 mA at a pulse duration of 2.5 msec). Following transesophageal DFT determination, in ten dogs (total energy of 600 ± 150 joules), acute esophageal histopathology demonstrated mild to severe focal injury to the mucosa and/or muscular layers. However, esophagi in four chronic dogs (total energy of 470 ± 110 joules) showed no gross evidence of macosal damage, perforation, or stricture 4 weeks following defibrillation. Histopathology showed only focal myocyte atrophy and repair. As a last resort, transesophageal defibrillation was performed in the emergency room on four patients with out-of-hospital refractory VF who failed > 6 high energy transthoracic shocks. Transesophageal defibrillation successfully terminated VF in each patient in spite of ≥ 50 minutes of cardiac arrest, however, none of the patients survived the initial resuscitation, Jn conclusion, transesophageal defibrillation is as effective as transthoracic defibrillation in a canine model and safe up to a total energy of 600 joules. Preliminary clinical trials suggest that this method results in conversion from VF when trunsthoracic defibrillation fails.     

Late Retesting of System Performance in ICD Patients Without Spontaneous Shocks

One hundred five implantable cardioverter defibrillator (ICD) patients (71 ± 9 years of age, 83% men) without spontaneous ICD discharges for ≥ 12 months were tested to assess high voltage (HV) circuit integrity and the system's ability to recognize and terminate ventricular fibrillation (VF). Indications for ICD implantation were sustained ventricular tachycardia (VT) (35%), cardiac arrest (27%), and inducible VT (38%). Eighty-two percent of the patients had coronary artery disease (CAD), and the mean left ventricular ejection fraction (LVEF) was 36%± 13%. Results: One hundred patients had inducible VF and five did not. Testing led to ICD reprogramming in 50 (49%) patients. Two (1.9%) patients required ICD replacement: (1) a 45-year-old patient with a Ventritex 110 ICD implanted for 13 months interfaced with a CPI 0062 lead implanted for 46 months could not be defibrillated internally (impedance nonmeasurable); (2) an 82-year-old patient with a 23-month-old Medtronic 7219 ICD interfaced with 6936 and 6933 leads whose defibrillation threshold (DFT) had doubled since implantation (24 J from 12 J). Lead fractures were found in both cases (proximal coil of the 0062, and subcutaneously in the 6933). Based on DFT determinations, the first shock output was programmed lower in 37 patients and higher in 10 patients. Shock pulse width was changed in one patient and the ventricular refractory period in another. No programming changes were made in 54 (51%) patients. Conclusions: (1) Late testing of HV circuit integrity in ICD patients without an ICD shock in ≥ 12 months identifies previously unsuspected HV lead fractures; (2) chronic DFT testing resulted in HV output reprogramming in one-half of the patients.     

Preliminary Clinical Results of a Biphasic Waveform and an RV Lead System

Biphasic defibrillation waveforms have provided a reduction in defibrillation thresholds in transvenous ICD systems. Although a variety of biphasic waveforms have been tested, the optimal pulse durations and tilts have yet to be identified. A multicenter clinical study was conducted to evaluate the performance of a new ICD biphasic waveform and new RV active fixation steroid eluting lead system. Fifty-three patients were entered into the study. Mean age was 63 years with a mean ejection fraction of 36.8%. Primary indication for implantation was monomorphic ventricular tachycardia alone (54.7%). Forty-eight patients (90.6%) were implanted with an RV shocking lead and active can alone as the anodal contact. The ICD can was the cathode. In four cases (7.5%), an additional SVC or CS had was used due to a high DFT with the RV lead alone. In an additional case, a chronic SVC lead was used although the RV-Can DFT was acceptable. DFT for all cases at implant was 9.8 ± 3.7 J. Repeat testing at 3 months for a subset of patients showed a reduction in DFT (7.4 ± 3.0 J), P value = 0.03. Sensing and pacing characteristics of the RV lead system remained excellent during the study period (acute 0.047 ± 0.005 ms at 5.4 V and 9.9 ± 6.2 mV R wave; chronic 0.067 ± 0.11 ms at 5.4 V and 9.3 ± 5.4 mV R wave). It is concluded that this lead system provides good acute and chronic sensing and pacing characteristics with good DFT values in combination with this waveform.     

Biphasic Defibrillation Using a Single Capacitor with Large Capacitance: Reduction of Peak Voltages and ICD Device Size

The volume of current implantable cardioverter defibrillators (ICD) is not convenient for pectoral implantation. One way to reduce the size of the pulse generator is to find a more effective defibrillation pulse waveform generated from smaller volume capacitors. In a prospective randomized crossover study we compared the step-down defibrillation threshold (DFT) of a standard biphasic waveform (STD), delivered by two 250-μF capacitors connected in series with an 80% tilt, to an experimental biphasic waveform delivered by a single 450μF capacitor with a 60% tilt. The experimental waveform delivered the same energy with a lower peak voltage and a longer duration (LVLDj. Intraopera-tively, in 25 patients receiving endocardial (n = 12) or endocardial-subcutaneous array (n = 13) defibrillation leads, the DFT was determined for both waveforms. Energy requirements did not differ at DFT for the STD and LVLD waveforms with the low impedance (32 ± 4Ω) endocardial-subcutaneous array defibrillation lead system (6.4 ± 4.4 J and 5.9 ± 4.2 J, respectively) or increased slightly (P - 0.06) with the higher impedance (42 ± 4 Ω) endocardial lead system (10.4 ± 4.6 J and 12.7 ± 5.7 /. respectively), However, the voltage needed at DFT was one-third lower with the LVLD waveform than with the STD waveform for both lead systems (256 ± 85 V vs 154 ± 53 V and 348 ± 76 V vs 232 ± 54 V, respectively). Thus, a single capacitor with a large capacitance can generate a defibrillation pulse with a substantial lower peak voltage requirement without significantly increasing the energy requirements. The volume reduction in using a single capacitor can decrease ICD device size.     

Clinical Experience with a New Cardioverter Defibrillator Capable of Biphasic Waveform Pulse and Enhanced Data Storage: Results of a Prospective Multicenter Study

A recently introduced cardioverter defibrillator was implanted in 162 patients with refractory ventricular tachyarrhythmias and/or aborted sudden cardiac death. The new device is capable of delivering monophasic and biphasic defibrillation waveform pulses, arrhythmia detection, and therapy in two independently programmable zones, antibradycardia and postshock pacing. Additionally, the device provides enhanced data logs by storing intracardiac “far-field” electrograms of spontaneous arrhythmic episodes. One hundred sixty-two patients (mean age 55.5 years; mean left ventricular ejection fraction 36%) were enrolled in this multicenter investigation; coronary artery disease was the primary cardiac disease in 63.6% of the patients, idiopathic cardiomyopathy in 23.8%. Ventricular fibrillation was present in 49.7% of the patients; 29.3% of the patients experienced ventricular fibrillation and ventricular tachycardia; monomorphic ventricuiar tachycardia alone was present in 19.1% of the patients. In 26 patients the device was implanted with standard epicardial defibrillation leads (mean defibrillation threshold 11.5±3.7J). One hundred thirty-nine patients underwent testing for implantation of a nonthoracotomy system and in 136 (98%), a nonthoracotomy system could be implanted. Defibrillation thresholds with a biphasic waveform (mean 10.2 ± 4.3 J) were lower than with a monophasic waveform (mean 17.4 ± 5.7 J). Two patients (1.2%) died perioperatively (< 30 days). During study time period follow-up, there were 338 device discharges in 49 patients. Analysis of stored electrograms classified 25% of discharges as inappropriate and due to supraventricular tachyarrhythmias. At a mean follow-up of 10.8 months, cumulative survival from sudden cardiac death was 98.8%, and survival from all-cause mortality was 96.3%. This study demonstates the effectiveness of a new implantable cardioverter defibrillator in preventing arrhythmic death and the superior defibrillation efficacy of biphasic waveform pulses, which results in a higher implantation rate of nonthoracotomy systems, as well as the accurate arrhythmia classification made possible by the stored electrograms.     

Initial Clinical Experience with a Dual Lead Endocardial Defibrillation System with Atrial Pace/Sense Capability

Ninety-three patients underwent implants of the Telectronics Model 4211 ICD attached to the Enguard PFX endocardial defibrillation lead system. Eighty-one males and 12 females ranging in age from 25–85 years (mean= 64). Coronary disease was the substrate in the majority (88%); mean left ventricular ejection fraction was 30%. VT was present in 66%, VF in 22%, and both in7%, Three lead configurations were used in the study: ventriculo-atrial (Ul, 86%); bidirectional (B2,12%); and ventricular to patch (U2, 2%). Mean RVpacing thresholds were 0.46 V preand 0.54 Vposttesting, with no significant differences between the two. Mean R wave voltage was 11.05 mVpreand 11.72 mV posttesting, also not significantly different. A subgroup of 13 patients had mean atrial pacing thresholds of 0.59 V at 0.5 msec pulse width, with mean P waves of 4.01 mV. Mean defibrillation threshold for the entire group was 10.6 J using biphasic waveforms. Defibrillation thresholds by configuration were: 399 V (U1);475 V(U2);and350 V(B2). All patients but one had thresholds ±550 V in at least one configuration. The 4211/Enguard system was implanted without (86%) or with (14%) a subcutaneous patch electrode. Early postoperative findings related to the ICD system include: one device circuit failure, one early lead dislodgement, and one pacing exit block. There were five patient deaths during the follow-up period of 8.5 months: three cardiac nonsudden and two noncardiac. These data suggest that the 4211/Enguard defibrillation system can be successfully implanted in the majority of patients in need of such therapy.